The present invention relates to improvements in the oxidation of liquid fuels. More particularly, the invention relates to combustion catalysts for organic liquid fuels, methods for using the catalysts in the combustion process, and fuels comprising the catalysts.
There has been considerable interest in recent years in developing new fuel additives and combustion catalyst systems for improving the combustion efficiency of gasoline, diesel fuel, and other organic liquid fuels, especially those derived from petroleum. One technique which is often used to measure combustion efficiency is to compare the heat produced to the amount of fuel used. The efficiency of any particular combustion process can also be measured by analyzing the oxidation reaction relative to a "target" reaction. By way of simple example, the complete oxidation of heptane under ideal conditions proceeds according to the following equation: EQU C.sub.7 H.sub.16 +110.sub.2 .fwdarw.7CO.sub.2 +8H.sub.2 O+Heat1
As can be seen from equation 1 above, the idealized complete combustion of a pure hydrocarbon fuel with pure oxygen produces only the reaction products of CO.sub.2, H.sub.2 O and heat. This can be viewed as a "target" combustion process. A more realistic equation representing the combustion of heptane on a commercial basis is represented by the unbalanced equation below: ##STR1## Referring to equation 2 above, the oxidation of heptane actually results in: (a) combustion gases containing CO, residual oxygen, and residual hydrocarbon; (b) heat production which is a fraction of the heat produced by the target combustion process; and (c) the undesirable production of NO.sub.x gas due to the use of air as the source of oxygen for the reaction.
The extent to which actual combustion approaches the reaction described by equation 1 is one measure of combustion efficiency. Accordingly, a desirable and effective combustion catalyst has the characteristics of providing increased energy output per unit of fuel consumed while also causing a reduction of the noxious gases produced in the combustion process. In particular, the amount of energy extractable from a given fuel should be maximized while the formation of hydrocarbon, carbon monoxide, and nitrous oxide emissions should be reduced or eliminated.
It is also highly desirable and advantageous for a combustion system to produce the above mentioned characteristics at a relatively low cost. Accordingly, it is generally desirable for fuel additives or catalysts to be required in only relatively small amounts, for example less than about one part catalyst to 500 parts fuel on a volume basis. In addition, it is greatly preferred that the materials which make up the combustion catalyst or liquid fuel additive have a cost which is a relatively low multiple of the cost of the fuel itself. For example, the materials should preferably have a cost which is no greater than about 3 times the cost of the fuel itself on a weight basis.
As noted above, the actual process of combustion or oxidation is very complex and is believed to proceed via many intermediate chemical species. Accordingly, it is frequently the case that combustion catalysts or liquid fuel additives are known to produce certain results, but the manner in which they function is not clearly understood. It is understood by those skilled in the art, however, that the advantages of and results obtained from any particular additive depend upon the particular combustion apparatus in use, the state of adjustment or repair of the apparatus, carbon build up in the apparatus from prior use, and factors of design. For example, current internal combustion engines are generally of a more efficient design than older models and will accordingly have a lesser potential for improvement in combustion efficiency.
Camphor and naphthalene have been used as gasoline additives to increase the performance of internal combustion engines. While certain improvements have been obtained from these materials, continuous operation of a combustion process using these components in liquid fuels is generally not desirable since they tend to have a severe negative impact on long term, overall combustion efficiency. This negative impact is manifested by increased production of carbon and soot in the process or apparatus.
Attempts have heretofore been made to eliminate the deleterious effects of camphor by providing a fuel oil additive containing both camphor and naphthalene in a mixture with a gasoline fraction, toluene, and benzyl alcohol. See U.S. Pat. No. 3,925,031--Villacampa. In particular, Villacampa discloses a fuel and oil additive which allows the addition of camphor on a continuous basis to a gasoline engine, allegedly without suffering any of the detrimental effects associated therewith. The additive disclosed in the Villacampa reference comprises an additive containing from 16 to 19.5 weight percent naphthalene, 6 to 8.7 weight percent camphor, 28 to 42 weight percent of a gasoline fraction, 36 to 45 weight percent toluene, and 1.0 to 3.0 weight percent benzyl alcohol. A major drawback of this formulation is the requirement of camphor in the composition. While camphor may impart some advantageous characteristics to the fuel additive, it is also generally the most expensive component thereof, often exceeding the cost of the fuel itself by 3000 percent on a weight basis. As a result, the requirement of including camphor as a component in the fuel additive is disadvantageous. In addition, due to the relatively large number of components required by Villacampa, the manufacturing costs associated with such material are relatively high.